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Total Disc Replacement
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Total Disc Replacement
- Ujwal Parikh
Scope
• Scope of the total disc replacement is to create a disc model that would improve the longevity and functionality of the implant to reduce pain.
Anatomy
• Human spine – 24 articulating vertebrae, 9 fused vertebrae.
• Stacked to form vertebral column maintaining human body’s upright posture.
• Each segment consists of vertebrae and spinal disc.
• Spinal Disc:– Nucleus pulpous (Jelly)– Annulus fibrosis (Stronger)
Anatomy
What is TDR?• Total Disc Replacement (TDR) is surgical
procedure replacing vertebral disc by an implant.
• Surgeon removes the worn-out, painful, degenerated disc replaces by metal implant.
• The goal is to reduce pain still maintaining complete functionality of spine.
• First clinical trial performed by Fernstorm in 1966 on 125 patients, 88% reduction.
CHARITÉ Artificial Disc (De Puy Spine, Inc.)
Why TDR?
• Degeneration of intervertebral disc in lower spine may lead to chronic back pain.
• The chronic nature results in reduced functionality hindering patient’s everyday life.
• Approximately 80% of Americans experience a significant back pain in their life time.
• Treatments– Anti-Inflammatory Medication– Surgical
I Spine fusion (Traditional)II Artificial Disc Replacement
Spinal Fusion Vs. TDR
Design Input
PRODISC® (Spine Solutions, New York, NY, USA)CHARITÉ Artificial Disc (De Puy Spine, Inc.)
L4-L5 vertebrae
Steps followed….
1. Plate2. Assembly3. Polymer4. Mechanical
Plate
Plate (Contd…)
Isometric View
Superior View Lateral View
millimeter
Breadth 42
A/P length 33
Thickness 4
Posterior radius 17
Anterior radius 11
Anterior View
Plate (Contd…)
Assembly
Polymer
Assembly + Polymer
Lateral ViewAnterior View
Isometric View
Material
Ti6Al4V
Young’s Modulus (E) 114 GPa
Poisson’s Ration (υ) 0.342
Density 4.43 g/ccTensile strength, Yield 880 MPa
Urethane Type L42
100 % Modulus 2.8 MPa
Poisson’s Ratio (υ) 0.48
Density 1.07 g/cc
Tensile Strength 20.7 MPa
Analysis
Polymer
Max. Stress 2.361 MPa
Max. Displacement 5.82 mm
Analysis (Contd…)
Plate
Max. Stress 1.167 MPa
Max. Displacement 8.246mm (10 deg)
Conclusion
• Since max. stress on polymer < tensile strength of Urethane L42, polymer won’t rupture
• Also max. stress on plate < yield strength of Ti6Al4V, metal wont break either for the given force and degree of freedom.
• For a force of 43.33 N, Angular displacement= 10 deg.• Stiffness = Moment/Angular Displacement
= 1.72 Nm/deg
References
• http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MTP641
• http://www.dsm.com/en_US/downloads/dbm/pdf002_-_Bionate_product_description-processing-properties.pdf
• http://www.americanurethane.com/aboutu1.htm• http://asm.matweb.com/search/SpecificMaterial.asp?
bassnum=MTP641• http://us.synthesprodisc.com/EN-US/• http://www.depuy.com/corporate-information/about-
depuy/history
Thank You